The invention relates to an arrangement for controlling the oil feed to a control chamber of a piston with variable compression height particularly for internal-combustion engines, which control chamber is arranged between an interior piston part and an exterior piston part that is slidably guided at it, and which control chamber is connected to the lubricating oil circuit of the internal-combustion engine, via an oil bore arranged in said interior piston part, into the course of which a check valve is inserted that opens in the direction of said control chamber, and which oil bore leads out into an oil groove in a connecting rod small end bush of the connecting rod shaft to a control oil groove in the connecting rod bearing, and via a transverse bore extending in the crank pin between the control oil groove and a main oil bore.
On the basis of German Published Unexamined Application (DE-OS) No. 34 16 346, it is known, in the case of a piston of the above-described type, to control the oil feed to the control chamber by means of a pressure-regulating valve that is integrated specifically into the hollow piston pin. The pressure-regulating valve is therefore constructed in such a way that, starting from a certain adjustable pressure difference between the control sides of the control slide, lubricating oil is directed from the longitudinal bore of the piston shaft into the oil bore in the interior piston part. As a result, mainly the pressure in the oil in front of the check valve can be kept constant irrespective of the pressure of the oil in the lubricating system.
One disadvantage with this above-noted arrangement is the manufacturing and mounting expenditures that are connected with the use of the pressure-regulating valve, and another disadvantage is the enlargement of the oscillating mass at the piston pin that results from that construction.
An object of the invention is to improve the known arrangement in such a way that, irrespective of a pressure-regulating valve within the oil bore and upstream of the check valve, an approximately constant oil pressure can be maintained in the incoming lubricating oil.
According to the invention, this objective is achieved in one preferred embodiment by providing that the control groove at the crank lifting journal bearing extends only over a portion of the circumference of the bearing so as to provide for connection with the lubricating oil circuit only over a predetermined portion of the piston stroke cycle. This objective is achieved in another preferred embodiment of the invention by appropriate cross-sectional area matching of the oil carrying grooves and bores.
By means of the invention, it is achieved that also, without the use of a pressure-regulating valve, the oil that is branched off from the lubricating-oil circuit for changing the compression height in the oil bore upstream of the check valve can be adjusted to a constant pressure. As a result of the elimination of the pressure-regulating valve, not only the oscillating mass of the piston is reduced, but the otherwise necessary manufacturing and mounting expenditures of the pressure-regulating valve are also eliminated.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.